How can I replace the drive belt on a qualcast power trak 34?

Specifically, I am struggling to remove the white belt drive cover. I've removed the blade and 4 screws from under the machine but the cover still won't move. Is there a hidden screw or other fixing that I don't know about? I've not been able to find a service manual online, the user manual is available but doesn't describe the inner workings. I would be grateful for any assistance.

Phil
March 2014